Black Carbon Sarah Rizk Environmental Scientist U.S. EPA Region 9, - PowerPoint PPT Presentation

Black Carbon Sarah Rizk Environmental Scientist U.S. EPA Region 9, Clean Energy and Climate Change Office Bay Area AQMD Advisory Council February 13, 2013

Outline  Basics & Definition  Inventories and trends  Climate forcing  Co-pollutants  Metrics  Mitigation  EPA work on Black Carbon (BC) Sources: EPA Report to Congress, recent Bounding Study (Bond et al. 2013)

Black Carbon Basics & Definition

www. epa.gov/blackcarbon

What is Black Carbon?  Black carbon is the most strongly light-absorbing component of particulate matter (PM). • BC is a solid form of mostly pure carbon that absorbs solar radiation (light) at all wavelengths.  BC is formed by incomplete combustion of fossil fuels, biofuels, and biomass.  Aggregate of small spheres  Insoluable in water and organic solvents  Short atmospheric lifetime 5

BC in the climate system a summary Warming of atmosphere decreases cloud cover, increasing solar radiation (+) Earth

Mixing State of Black Carbon Sulfate • Freshly emitted BC particles are externally mixed, whereas aged BC particles are mostly mixed internally Black • Carbon Internal mixing of BC alters its aggregate shape, hygroscopic, and optical properties • Knowledge of mixing state of BC External Mixture containing particles is important for  Calculating their radiative forcing  Providing insight into their source and life cycle Internal Mixture 7

Health Effects of Black Carbon  Health effects associated with BC are consistent with those associated with PM 2.5 .  Includes respiratory and cardiovascular effects and premature death.  Emissions and ambient concentrations of directly emitted PM 2.5 are often highest in urban areas, where large numbers of people live.  Average public health benefits of reducing directly emitted PM 2.5 in the U.S. are estimated to range from $290,000 to $1.2 million per ton PM 2.5 in 2030.  Globally, BC mitigation measures could potentially lead to hundreds of Brick Kiln in Kathmandu thousands of avoided premature deaths each year. 8 EPA Report to Congress

Near-term climate benefits Temperature ( ° C) relative to 1890-1910 Reference Reference LLGHG mitigation LLGHG CH 4 and BC mitigation mitigation CH 4 and BC mitigation LLGHG, CH 4 and BC mitigation LLGHG, CH 4 and BC mitigation 1900 2000 1950 2050 UNEP/WMO Integrated Assessment of BC and Ozone, 2011; Shindell et al. Science , 2012 9

Black Carbon Inventories & Trends

Black Carbon Emissions (580 Gg) EPA Report to Congress  75% of global BC emissions come from Asia,  In the U.S., BC emissions ~12% of Africa and Latin America. all direct PM 2.5 emissions nationwide.  U.S. currently accounts for approximately 8% of  Mobile sources are the largest U.S. the global total, and this fraction is declining. BC emissions category (with 93% of mobile source BC coming from  Emissions patterns and trends across regions, diesels). countries and sources vary significantly. 11

State Inventories for Black Carbon Top 15… *nonattainment PM2.5 (2006 Std) Black Carbon is ~10% of PM2.5 nation-wide

Black Carbon Emissions: Global Trends  Long-term historic trends of BC emissions in the United States and other developed countries reveal a steep decline in emissions over the last several decades.  Ambient BC concentrations have declined as emissions have been reduced.  Developing countries (e.g., China and India) have shown a very sharp rise in BC emissions over the past 50 years.  Total global BC emissions are likely to decrease in the future, but developing countries may experience emissions growth in key sectors (transportation, residential). 13 EPA Report to Congress

Black Carbon Climate Forcing

EPA Report to Congress: Total BC forcing uncertain EPA Report to Congress

Bounding Study: BC Forcing is net warming; best estimate is that it’s second only to CO 2 CO 2 CH 4 N 2 O Bond et al. AGU 2013

Direct forcing  Most estimates of direct forcing have been too low • Bounding-BC: +0.71 W/m2 • IPCC AR4: +0.34 W/m2 obs higher than obs lower than model model  There is more absorption in the real atmosphere than in the simulations • More in line with previous Ramanathan & Carmichael • Causes are evaluated and attributed to regions  Large uncertainties • (+0.08 to +1.27 W/m 2 – 90% confidence) 17 unshaded part of bar may be caused by “internal mixing” Bond et al. AGU 2013

Total forcing  Best estimate of total forcing +1.1 W/m 2 • More warming than BC alone  Cloud indirect: +0.18 W/m 2 • Liquid clouds negative, but there are other effects  Snow & sea ice: +0.13 W/m 2  Very large uncertainties • Especially from clouds • Few models of some types of clouds • Few observational constraints  Despite uncertainties, BC is net warming 18 Bond et al. AGU 2013

Accounting for Co-pollutants

Co-emitted species NOx  Sources that emit black carbon OC also emit other short-lived species CO that affect climate BC  Sulfate: COOLING CO2  Organic carbon: COOLING  Gases: WARMING or COOLING  Shutting off a source entirely removes all species 20 Bond et al. AGU 2013

Analysis for Total BC-rich source Total categories Total Total Short-lived species only Total  Some categories are net positive (red) Total  Some are net negative Total (blue) Total  Some are uncertain – Total sign unknown Total 21 Bond et al. AGU 2013

Long-lived & Short-lived Climate forcers  Short-lived forcing (red)  Long-lived forcing (blue)  Sometimes additive, sometimes negate each other 22 Bond et al. AGU 2013

My own preliminary analysis in California

Black Carbon Climate Metrics

Black Carbon Climate Metrics  Different types of climate equivalency metrics place value on different attributes EPA Report to Congress  The choice of the time horizon is also an important one 25

Black Carbon Climate Metrics Integrates climate impact over time The effect of a “pulse” reduction on temperature 26 Bond et al. AGU 2013

Considerations for choosing & applying a metric Look for win-wins : What are the mitigation strategies that maximize reductions of both LLGHG 1. and SLCF? 2. Consider institutional priorities: Determine whether the focus of the institution has a greater emphasis on LLGHGs (may want to use a lower bound equivalency value for BC) or on SLCFs (may use an upper bound equivalency value for BC). In most cases, organizations will want to evaluate options with a range of values. More emphasis on LLGHGs More emphasis on SLCFs Reduce temperature Delay impacts in the near term the long term and risk of tipping points Decrease global impacts Decrease local impacts Maximize climate benefit Maximize health benefit Not willing to accept Willing to accept some uncertainty in climate remaining uncertainties in forcing climate forcing Analyze the decision: What’s the level of investment in the program? For high investment 3. programs, use a wider range of values . Use a sensitivity analysis to see whether the outcome 27 changes with the full range of equivalency values used.

Black Carbon Mitigation Opportunities

Mitigating BC: Key Considerations  For both climate and health, it is important to consider the location and timing of emissions and to account for co-emissions.  Available control technologies can reduce BC, generally by improving combustion and/or controlling direct PM 2.5 emissions from sources.  Some state and local areas in the U.S. have already identified control measures aimed at direct PM 2.5 as particularly effective strategies for meeting air quality goals.  Though the costs vary, many reductions can be achieved at reasonable costs. Controls applied to reduce BC will help reduce total PM 2.5 and other co-pollutants. 29

U.S. Residential Heating and Cooking  Emissions from residential wood combustion are currently being evaluated as part of EPA’s ongoing review of emissions standards for residential wood heaters, including hydronic heaters, woodstoves, and furnaces.  Mitigation options include replacing or retrofitting existing units, or switching to alternative fuels such as natural gas. • New EPA-certified wood stoves have a cost- effectiveness of about $3,600/ton PM 2.5 reduced, while gas fireplace inserts average $1,800/ton PM 2.5 reduced (2010$). 30

Open Biomass Burning  Open biomass burning is the largest source of BC emissions globally, and these emissions have been tied to reduced snow and ice albedo in the Arctic. • A large percentage of these emissions are due to wildfire (e.g., U.S. Alaskan fires). • Total organic carbon (OC) emissions (which may be cooling) are seven times higher than total BC emissions from this sector.  PM 2.5 emissions reductions techniques (e.g., smoke management programs) may help reduce BC emissions.  Appropriate mitigation measures depend on the timing and location of burning, resource management objectives, vegetation type, and available resources.  Expanded wildfire prevention efforts may help to reduce BC emissions worldwide. 31

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